1. Field of the Invention
The present invention relates to an accumulator which is used as a pressure accumulator or a pulse pressure damping device. The accumulator according to the present invention is used, for example, in an automotive hydraulic system or a hydraulic system for an industrial device.
2. Description of the Conventional Art
Conventionally, as shown in FIG. 11, there has been known an accumulator 51 structured such that an accumulator housing 52 is provided with an oil port 53 which is connected to a pressure piping (not shown), and is provided with a gas charging port 54, an internal space of the accumulator housing 52 is comparted into a gas chamber 57 which is filled with gas by a bellows 55 with a bellows cap 56 and a liquid chamber 58 which is communicated with the oil port 53, and the accumulator 51 is activated in a pressure accumulation manner or is activated in a pulse pressure damping manner on the basis of a movement of the bellows cap 56 and an expanding and contracting motion of the bellows 55 so that the gas pressure and the liquid pressure are balanced (refer to Japanese Unexamined Patent Publication No. 2003-172301).
Further, the accumulator 51 is provided with a safety mechanism (a safety mechanism for a pressure reducing time) 59 which prevents the bellows 55 from being broken due to an unbalance between the gas pressure and the liquid pressure, in the case that the pressure of the pressure piping is reduced and the pressure of the liquid chamber 58 is reduced. In other words, in the case that the pressure of the pressure piping is reduced extremely due to stop of an operation of the device, the liquid (the oil) is discharged little by little from the oil port 53. As a result, the bellows 55 is accordingly deflated little by little by the charged gas pressure, and a seal 60 provided in a lower surface of the bellows cap 56 comes into contact with a stay 61 so as to come to a so-called zero-down state. The stay 61 is a single metal molded product in which a liquid port opening 61c is provided in an end surface portion 61b in a leading end of a tubular portion 61a. Further, in the zero-down state, a part of the liquid is confined in the liquid chamber 58 by the seal 60, and since the pressure of the confined liquid and the gas pressure of the gas chamber 57 are balanced, it is possible to inhibit the excessive stress from being applied to the bellows 55 and inhibit the bellows 55 from being broken.
Further, the accumulator 51 is provided with a safety mechanism (a safety mechanism for an emergency) 62 which prevents the liquid within the liquid chamber 58 and the gas within the gas chamber 57 from being rapidly inflated and prevents the accumulator 51 from being exploded, in an emergency such as a fire disaster occurrence. In other words, in the case that the liquid within the liquid chamber 58 and the gas within the gas chamber 57 are rapidly inflated due to the occurrence of the fire disaster, a rupture plate (a vulnerable part) 61d provided locally and circumferentially on a peripheral surface (the tubular portion 61a) of the stay 61 is ruptured due to the high pressure, and the high pressure is released. Therefore, an inner portion of the accumulator 51 is inhibited from becoming extremely high pressure so as to cause an explosion.
However, in the prior art mentioned above, since the safety mechanism 62 for the emergency is constructed by the rupture plate 61d which is locally and circumferentially provided on the peripheral surface (the tubular portion 61a) of the stay 61 as mentioned above, the rupturing pressure is high (such a high pressure as to rupture the metal plate is necessary). As a result, there is a disadvantage that the safety mechanism 62 for the emergency is not activated until the pressure becomes very high. Further, in order to provide the circumferential and local rupture plate 61d on the peripheral surface (the tubular portion 61a) of the stay 61, it is necessary to additionally execute a cutting process after press molding the stay 61. As a result, there is a disadvantage that a lot of labor hour and time are required for manufacturing the stay 61.